In the photoresist processing step in, for example, the manufacture of semiconductor devices, a substrate, such as a semiconductor wafer (hereinafter, referred to as a wafer), is washed and the surface of the wafer is coated with a photoresist solution to form a photoresist film. After the photoresist film is exposed using a specific pattern, the exposed film is developed with a developing solution. To carry out such a series of processes in the photoresist processing step, a photoresist coating and developing system has been used.
The photoresist coating and developing system includes a cassette table on which a plurality of cassettes are placed in alignment and a transfer mechanism that takes out one of the wafers from the cassette table and conveys it to a main transfer arm. The cassettes are each a container for housing a plurality of wafers. The transfer mechanism can move freely over a transfer path laid in the direction of cassette arrangement (in the direction of X). Various processing machines that perform specific processes on a wafer are arranged on both sides of the transfer path for the main transfer arm. Specifically, on both sides of the transport path, there are provided a brushing machine for brushing a wafer while turning it, a washing machine for washing a wafer W with a high-pressure jet of water, an adhesion processing machine for improving the fixation of resist by subjecting the surface of the wafer to an adhesion process, a cooling machine for cooling the wafer to a specific temperature, a photoresist coating machine for coating the surface of the rotating wafer with a resist solution, a heater for heating the photoresist-coated wafer or the pattern-exposed wafer, and a developing machine for developing the exposed wafer by supplying a developing solution to the wafer's surface, while rotating the wafer.
There is also provided an interface section that transfers the wafer on which the specific photoresist film has been formed to a pattern exposure machine (i.e., optical stepper) located outside the photoresist coating and developing system. The interface section includes a table section on which the wafer transported by the main transfer arm is to be placed, and a wafer passing mechanism for conveying the wafer between the table section and the loading/unloading section of the exposure machine. The wafer passing mechanism has a similar function to that of the transfer mechanism. That is, it can not only move along the transfer path (in the direction of X), but also move back and forth in the direction of Y and rotate in the direction of 0 in an X-Y plane.
In the conventional photoresist coating and developing system, the loading of an unexposed wafer into the exposure machine and the unloading of the exposed wafer from the exposure machine are effected through the loader/unloader section in the exposure machine.
In recent years, various types of exposure machines have been developed. Some of them have a suitable loading/unloading arm instead of a loader/unloader section in their exposure machine. The loading/unloading arm in the exposure machine is designed to advance to and retreat from the interface section and thereby load the wafer in the interface section into the exposure machine and returns the exposed wafer in the machine to the interface section.
The conventional processing system, however, cannot deal with the exposure machine constructed as described above. Because the pattern exposure machine is installed outside the processing system, the height of the system and that of the exposure device have to be adjusted for a smooth transfer of a wafer between them. This type of processing system is designed to perform a series of processes within the system as much as possible by adding various functions to the system. At the same time, it is desirable that the necessary installation space should be as small as possible. In the future, as the diameter of a wafer, a substrate, will get larger, minimizing the necessary installation space will probably be a pressing need.